EAS systems have been in use for many years as a means of aiding the deterrence of theft in various types of retail establishments. One common type of EAS device involves the use of a small sensor tag comprised of durable material. The tag is affixed to the object to be monitored in such a way as to prevent easy, unauthorized removal of the tag. The EAS device is usually constructed and attached in such a way that it can only be removed from the object being monitored by specialized tools in the possession of authorized store personnel. In the event that an EAS monitoring device is not deactivated, or if it is removed from the retail establishment by unauthorized personnel, an alarm or other signal is activated. An alarm or other signal is likewise activated upon the unauthorized removal of the EAS device from the object being monitored, while the object being monitored is still within the retail establishment.
In many commercially available EAS systems, one or more antennas are placed at or near exits and entrances to the retail establishment. These antennas set up what are sometimes called interrogation zones, in which an EAS device may be sensed. At least one antenna serves the function of sending out what is called an interrogation signal. The EAS device, to which the object being monitored is attached, is affected by this signal and may respond with a signal of its own. Either the same antenna that sends out the interrogation signal or other additional antennas can sense the signals from the EAS device. The most effective way to do this is by stopping the broadcast of the interrogation signal to listen for the signals emanating from the EAS device. If an EAS device is sensed within the interrogation zone created by the antennas, it is presumed that a monitored object is being removed from the retail establishment without proper authorization, and alarms are set off. These alarms may be audible for general broadcast, or the alarms may be silent alarms in the form of a light at a security station, etc. Additionally, some EAS devices have onboard audible alarm generators and can generate audible alarms by themselves. These EAS devices may produce this audible alarm when onboard logic elements determine that the EAS device is being removed from the retail establishment, or when the larger EAS system communicates to the EAS device to alarm. The onboard logic elements and the larger EAS system may also cause the EAS device to cease to alarm under certain situations.
A common manner of attempting to defeat an EAS device is to forcibly disengage it from the object to be monitored. A counter-measure which may be employed by an EAS device is the introduction of a switch which has its state changed and arms, or pre-arms, the EAS device when it is releasably attached to, or joined with, an object to be protected. For example, a switch can be positioned on the EAS device in such a manner that the object bears upon the switch and changes the switch's state when the EAS device and the object are joined together. Alternatively, for EAS devices comprised of multiple pieces, the switch may be located on one piece of the EAS device, and another piece of the EAS device may change the state of the switch when the EAS device is joined with the object to be monitored.
Associated devices may communicate with electronics within the EAS device to add an additional step to the device's arming process. When the EAS device is attached to the object to be monitored and the state of the switch is changed, this change of state functions to confirm that the EAS device is installed/attached, and authorized persons can use an associated device to wirelessly communicate with the EAS device to complete the process of arming the EAS device. Once armed, if the EAS device is forcibly disengaged from the object to be monitored, or if the EAS device is removed from the object to be monitored by an unauthorized person, the switch's state changes again, and the electronics of the EAS device determine that an alarm condition exists. The EAS device can sound an audible alarm with an onboard audible alarm generator, or wirelessly communicate an alarm to other elements of the EAS system.